1. Field of the Invention
The present invention relates to an ink tank used in a printing apparatus performing a printing operation by ejecting a printing liquid such as ink. In particular, the invention relates to a configuration of an ink tank which prevents problems such as leakage of ink while stably supplying ink to a printing head even when the tank has a change in the internal pressure thereof or when the tank is vibrated during transportation.
2. Description of the Related Art
Ink jet printing apparatus are what are called non-impact type printing apparatus. They are characterized by capability of high-speed printing and capability of performing printing on various printing medium and characterized in that they make substantially no noise during printing. Therefore, ink jet printing apparatus are widely used as primary apparatus to serve as printing mechanisms of printers, word processors, facsimile machines, and copiers.
Such an ink jet printing apparatus has a printing head for ejecting ink on to a printing medium and an ink tank for intermittently supplying ink to the printing head. While the printing head and the ink tank are integrally formed in some configurations, the printing head and the ink tank are formed as separate bodies so that the ink tank is allowed to be detachably attached to the printing head which is mounted in a printing apparatus.
FIG. 6 is a perspective view of an exemplary ink jet cartridge having the former type of configuration, i.e., a configuration in which a printing head and an ink tank are integrally formed. Referring to FIG. 6, an ink jet cartridge 1000 is primarily formed by an ink tank section 1200, a printing head section 1100, and an electrical wiring substrate 1300. Ink contained in the ink tank section 1200 is supplied to the printing head section 1100 and ejected from the printing head section 1100 according to a printing signal input from the electrical wiring substrate 1300.
Various types of ejection mechanisms usable in the printing head section 1100 have been proposed. For example, the printing head section 1100 may be provided with a plurality of printing elements each including a heating element, an ink path for guiding ink to the heating element, and an ejection opening serving as an exit of the ink path. In this case, the following mechanism works. The heating elements generate heat when a voltage pulse input through the electrical wiring substrate 1300 is applied to the same. Film boiling occurs in ink in contact with the heating elements, and the growing energy of the resultant bubbles ejects the ink through the ejection openings.
FIG. 7 is an exploded perspective view of the ink jet cartridge 1000, and FIG. 8 is a sectional view taken along the line VIIIA-VIIIA in FIG. 6. A tank case 1400 contains an absorbing body 1700 for absorbing and holding ink and has a mechanism for supplying the ink to a printing element substrate 1500 forming a part of the printing head section. A recess for accommodating the printing element substrate 1500 is formed on a bottom surface of the tank case 1400, and an ink flow path 1401 to serve as a path for supplying ink to the printing element substrate 1500 is provided in the middle of the recess. A filter 1600 is disposed at the bottom of the interior of the tank case 1400 and on the side of the tank case where the ink flow path is provided. The filter prevents foreign substances which have entered the tank case from flowing into the ink flow path 1401 or toward the printing element substrate 1500.
The tank case 1400 is closed by a lid member 1800 on the top side thereof. The absorbing body 1700 is pushed downward by ribs 1808 provided on the lid member 1800 to form spaces 1402 in the tank case 1400. The lid member 1800 has an atmospheric communicating port 1801 substantially in the middle thereof to provide communication between the spaces 1402 formed by mounting the lid member 1800 and the atmosphere.
FIG. 10 is a view of a top surface of the lid member 1800 taken when a sheet member 1900 is not applied thereto. The atmospheric communicating port 1801 located substantially in the middle of the lid member 1800 is connected to an atmospheric communicating channel 1803 formed as a maze-like groove on the surface of the lid member 1800. The sheet member 1900 is applied such that an end of the atmospheric communicating channel 1803 is left uncovered as shown in FIG. 9 to form an atmospheric communicating channel exit 1802.
As thus described, a mechanism for providing communication between the interior of the tank case 1400 and the atmosphere is provided to suppress fluctuations of an internal pressure which may be caused by gradual consumption of ink as a result of an ejecting operation. Thus, ink can be supplied to the printing element substrate 1500 with stability. However, the provision of the atmospheric communicating port 1801 as thus described may promote the evaporation of the ink in the ink tank. Therefore, it is required to design the channel for atmospheric communication so as to keep the evaporation of the ink in the tank case as small as possible while maintaining the communication between the interior of the tank case and the atmosphere. The amount of ink evaporating through the atmospheric communicating channel is proportionate to the sectional area of the atmospheric communicating channel 1803 and inversely proportionate to the length of the channel. Therefore, the above-mentioned requirement is met by a narrow and long atmospheric communicating channel having a complicated pattern as shown in FIG. 10.
The internal pressure of the tank case 1400 fluctuates as a result of not only printing operations but also changes in ambient conditions. When there is an abrupt change in the internal pressure or a great change in posture of the ink cartridge, ink may flow out through the atmospheric communicating port. It is therefore required to design the ink tank so as to prevent ink from flowing out from the atmospheric communicating port and to prevent the ink from leaking out to exterior of the tank in case ink flows out from the port.
Japanese Patent Laid-Open No. H05-318759(1993) discloses an ink jet cartridge having an ink reservoir member made of fiber provided in an ink tank to prevent ink from leaking out through an atmospheric communicating port by storing ink flowing from an absorbing body in the reservoir member. In the configuration disclosed in Japanese Patent Laid-Open No. H05-318759(1993), the ink reservoir member and the absorbing body are connected through an ink wick constituted by a fiber bundle. Even when there is a change in the posture of the cartridge, ink can be held by the ink wick without closing the atmospheric communicating port. It is therefore possible to prevent ink from leaking out even if there is a pressure change or a temporary shock.
Japanese Patent Laid-Open No. H10-278290(1998) discloses an ink jet cartridge having a configuration in which a recess for storing ink is formed in an atmospheric communicating channel to increase the amount of ink which can be stored in the atmospheric communicating channel.
In the case of the configuration disclosed in Japanese Patent Laid-Open No. H05-318759(1993), since the ink reservoir member and the absorbing body are connected through the ink wick constituted by a fiber bundle, ink tends to migrate from the absorbing body to the ink reservoir member because of the nature of the configuration. As a result, for example, when vibrations are continuously imparted to the cartridge in an inverted posture, the ink reservoir member can be saturated with ink, and leakage of ink can thereafter occur. Further, since the ink reservoir member has a complicated configuration, the ink tank itself may become problematically expensive.
In a configuration as disclosed in Japanese Patent Laid-Open No. H10-278290(1998) in which an ink reservoir is locally provided to store a great amount of ink, when the posture of the ink tank changes while ink is stored in the ink reservoir, ink flow-out can take place. The reason is that no force acts on the ink reservoir so as to allow the ink to be held against the change in posture. Further, communication between the interior of the tank case and the atmosphere is hindered when ink is stored in the atmospheric communicating channel. Thus, when the pressure in the tank case increases as a result of a temperature change or the like, the ink in the ink reservoir can leak out. The reason is that the atmospheric communicating channel is closed by the ink stored in the same.